noun
downy hair; peach fuzz; vellus hair
Fine, soft hair on the body, especially of a baby or on areas not normally covered by terminal hair. In everyday language, often called 'peach fuzz'.
赤ちゃんのほっぺたには産毛が生えている。
The baby's cheeks are covered with downy hair.
彼女の腕には金色の産毛がうっすらと見えた。
Fine golden hairs were faintly visible on her arms.
noun
lanugo
Medical/biological term for the fine hair covering a fetus or newborn. In non-specialist contexts, sense 1 is used.
産毛は胎児の体を保護する役割がある。
Lanugo serves to protect the fetus's body.
Compound of 産 (うぶ, 'birth, newborn') + 毛 (け, 'hair'), with rendaku voicing. Refers to the fine hair present at birth.